This application claims the priority of German application 101 54 091.4, filed Nov. 2, 2001, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method and a system for controlling a cooling system of an internal-combustion engine, also referred to as an engine in the following.
Such a cooling system includes a coolant pump which guides coolant through an internal-combustion engine in order to cool the latter.
It is known that a coolant pump can be connected, for example by way of a V-belt, with the crankshaft of an internal-combustion engine so that the pump is driven along with engine operation.
Furthermore, a method is known from German Patent Document DE 195 08 104 C2 for controlling a cooling circuit of an internal-combustion engine in which a differentiation is made between a warm-up phase, an operating phase and after running. The warm-up and operating phases, when the engine is started, are determined by the coolant temperature at the engine exit, which is compared with a coolant temperature limit value for the warm-up phase. When the coolant temperature falls below that value, the warm-up phase is recognized. When that value is reached or exceeded, the operating phase is recognized. In the warm-up phase, the engine is at first not cooled as long as it has not reached a coolant starting temperature. After this starting temperature has been reached, however, an air flow generated by a fan, which is guided through a radiator module, and the coolant flow generated by the coolant pump are controlled as a function of a desired difference temperature value of the coolant between the engine inlet and exit. An actual difference temperature value required for the control is determined by way of the heat flow from the internal-combustion engine into the coolant. The heat flow, in turn, is calculated from the momentary coolant flow, the momentary engine load and the rotational engine speed. In this case, the rotational speed of the coolant pump changes with the change of the heat flow, so that brief engine load or rotational speed changes do not affect the operation of the coolant pump. As soon as the temperature limit value for the warm-up phase has been reached, the so-called operating phase will start. During this operating phase, control of the coolant pump and of the fan takes place as a function of the desired difference temperature value and of a desired temperature value of the coolant at the engine exit. The desired temperature value is determined by way of a corresponding characteristic diagram for a defined engine temperature. In the after running phase, in which the engine is switched off, the engine continues to be cooled if the coolant temperature exceeds a predetermined temperature limit value. This method has the disadvantage that the temperature or the difference between various temperatures in the cooling system is used as the control value. Such temperatures in the cooling circuit are slow and, lastly, are only effects of the engine or vehicle operating point.
In European Patent Document EP 0 952 315 A1, a control system for minimizing consumption of electric energy in a cooling system of an internal-combustion engine is disclosed. Based on the engine temperature, vehicle speed and ambient temperature detected by sensors, a control unit controls a fan and an electric pump for cooling the internal-combustion engine. By way of the values detected by the sensors, an operating point is determined by using a characteristic diagram in order to discharge a certain amount of thermal energy from the engine which indicates an optimal ratio from the sum of the energy fed to the fan and the pump. The control system has the disadvantage that several sensors are required in order to detect certain parameters as a function of which the engine is cooled. In addition to the costs which are connected with each individual sensor, there is also the risk of a breakdown of the latter. Likewise, in the case of temperature measuring points, the measuring precision may be reduced by external influences, and a control on the basis of the temperature is therefore limited.
It is an object of the invention to provide a method and a system for controlling a cooling system of an internal-combustion engine in which reliable cooling is permitted.
According to the invention, this object is achieved by a method for controlling a cooling system of an internal-combustion engine including controlling a capacity of a coolant pump as function of a fuel quantity fed to the internal-combustion engine. This object is also achieved by a system for controlling a cooling system of an internal-combustion engine having a coolant pump including a control device which controls a capacity of a coolant pump as a function of a fuel quantity fed to the internal-combustion engine.
One idea of the invention is the idea of variably controlling the cooling system and the variably drivable coolant pump connected therewith as a function of a fuel quantity supplied to the engine. The capacity of the coolant pump can be adjusted over a range of from preferably zero to a maximal pumping capacity (l/h), either continuously or variably, in a plurality of steps. Since the quantity of fuel supplied to the internal-combustion engine is related to heating of the engine, control of the coolant pump, and thus cooling of the engine, can take place in a foreseen manner on the basis of the actually consumed fuel. The relationship of engine heat feeding into the coolant to the fuel mass flow is largely similar for all combustion concepts. This has the advantage that the cooling system or the coolant pump can be controlled according to originator quantities and not solely, as is known, by temperatures in the cooling circuit which are slow and, in addition, are only the effects of an engine or vehicle operating point. Another advantage is that a cooling control is basically possible without sensors or temperature measuring points which are susceptible to disturbances, and these sensors or temperature measuring points, as required, are used only in warm-up, hot idling or hot shut-off operating situations.
Advantageous developments are reflected in certain claims.
According to a preferred embodiment of the invention, the sum of the fed fuel quantity since the ignition of the engine xcexa3mxe2x80x2KS is compared with a so-called desired fuel quantity mdesired. If the fed fuel quantity falls below the desired value, as occurs, for example, during a cold start of the engine, at first, cooling of the engine by the cooling system does not take place, unless by way of a volume flow demanded for other needs in the cooling system, for example, for a heater. This has the advantage that the warm-up phase of the engine can be shortened and the fuel consumption can be reduced as compared to engines in which the coolant pump is connected with the crankshaft. In the case of these engines, the coolant pump is automatically driven with the starting of the engine, so that the engine is cooled before it is warmed up.
If the sum of the fed fuel quantity xcexa3mxe2x80x2KS exceeds the given desired value mdesired, cooling takes place by switching the coolant pump on. In this case, the capacity of the coolant pump is determined as a function of at least one parameter, such as the rotational engine speed nMot, the engine load, the outside temperature and/or an average value for a predetermined time interval (for example, 30 seconds) of the fuel quantity mxe2x80x2KS. By way of a time-related averaging of the coolant pump rotational speed, compressive pulsating stress can be avoided. This leads to lower stressing of the cooling system and the water or other coolant pump.
Preferably, the cooling system and the coolant pump are additionally controlled as a function of the coolant temperature. For this purpose, in addition to the comparison of the fed fuel quantity, the momentary temperature of the coolant TMot is compared with a desired coolant temperature Tdesired. If the desired value Tdesired is exceeded, cooling of the engine by the cooling system takes place, in which case the capacity of the coolant pump, as described above, can be determined as a function of the rotational engine speed nMot, the engine load, the outside temperature and/or the average value of the fuel quantity mxe2x80x2KS. This has the advantage that the operating point of the coolant pump can furthermore be variably adapted as a function of defined parameters, such as the outside temperature or the load. This operation is particularly advantageous during hot idling and hot shut-off of the engine.
In addition or as an alternative, the cooling system and the coolant pump can be controlled as a function of the engine oil temperature. For this purpose, in addition to the comparison of the fed fuel quantity, the coolant temperature, the momentary engine oil temperature Toil, is compared with a desired engine oil temperature Tdesired. When the momentary engine oil temperature falls below the desired value Tdesired, cooling by the coolant pump does not take place, unless by way of a volume flow demanded for other requirements in the cooling system, for example, for a heater. Furthermore, the cooling starts as soon as the desired engine oil temperature Tdesired is exceeded. In this case, the capacity of the coolant pump is determined as a function of the rotational engine speed nMot, the engine load, the outside temperature and/or an average value of the fuel quantity mxe2x80x2KS.
In addition to the coolant pump, the operation of additional devices, such as an air conditioner, a separate heater or an automatic transmission, also withdraws heat from and/or feeds heat to the engine. Consequently, control of the cooling system preferably additionally takes place as a function of the connecting or the heat feeding of such a device. Here, the capacity of the coolant pump is preferably determined as a function of a connection degree, for example, of the heater. It is advantageous that the pump is operated corresponding to the demands of the additional device, even if this would not be necessary for cooling of the engine. This is the case, for example, for supplying the heating or cooling of the automatic transmission, for example, during idling. As a result, an additional water pump for the heater may not be required under certain circumstances. Corresponding to a connection degree of the heater, for example, of approximately 100%, the capacity of the coolant pump is increased, so that the latter can pump a portion of the coolant to the heat exchanger of the heater. If no heater is connected, the previously defined capacity of the coolant pump is maintained.
Furthermore, the control system compares a first coolant temperature threshold value with the momentary coolant temperature TMot. If the threshold value is exceeded, the coolant pump is operated at least within a predetermined time interval at a predetermined capacity, so that the engine continues to be cooled. This has an advantage in that the engine is sufficiently cooled when running hot or under additional heating by the ambient temperature.
In order to permit reliable cooling in the case of a hot shut-off of the engine after a high load, it is determined whether the engine is shut off. If, in this case, the coolant temperature exceeds a second coolant temperature threshold value, the coolant pump will be operated at a predetermined capacity within a predetermined time interval, and the engine is cooled. This has the advantage that the engine continues to be cooled, and temperature peaks in the engine after the shut-off of the engine after a high load can therefore be prevented. The duration of after running therefore depends on the temperature exceeding the desired value, in which case a defined duration should not be exceeded (discharge of the battery). When the coolant temperature falls below the second coolant temperature threshold value, no further cooling by the cooling system takes place.
When it is determined that the engine is operative, the control circuit is closed, and another calculation of pump capacity takes place by way of the fed fuel amount in order to achieve continuous cooling of the engine.
An embodiment of the invention will be described in detail with reference to the drawing.